In the field of ophthalmology, there has been an increase in the use of contact lenses for ocular diagnosis and in various forms of ocular therapy. In this regard, a number of special contact lens instruments have been developed to assist the ophthalmologist or optometrist in the observation of the eye for diagnosis of eye disease, or in the performance of ocular surgical techniques and treatment. Such diagnostic or therapeutic contact lenses have significantly distinct characteristics that differentiate them from prescription contact lens which are used to correct refractive error of a patient's eye and thus achieve improved visual acuity.
In the use of a contact lens as an aid to vision, the front surface of the lens will act as a substitute for the anterior surface of the cornea, such that the lens may correct the irregularities of the front surface of the cornea which would not be correctable using conventional spectacles. In addition, the principle type of contact lens in current use corrects the usual refractive errors which also would be correctable with spectacles. In the development of contact lenses as an aid to a patients vision, emphasis has been placed upon eye health as well as the comfort with which such lenses can be worn. For example, until the latter part of the 1940's, almost all contact lenses utilized to aid vision had a portion resting directly on, or arching over, the cornea, with a supporting flange resting beyond the limbus on the sclera of the eye. Such lenses were referred to as scleral lenses, and were normally constructed of a glass material.
Subsequently, the feasibility of using plastic for lens fabrication was demonstrated with the introduction of a methyl methacrylate plastic molded scleral contact lens. The use of plastics led to the "hard" plastic corneal contact lens, which provided a lens of smaller diameter positioned within the limbal area of the cornea. These plastic materials, such as poly-methyl methacrylate (PMMA) had hydrophobic properties which reduced safe wearing time and may have caused discomfort to the wearer. The desired aspect of comfort, extended wearing times and eye health led to further developments, such as the development of soft "hydrophilic" gel lenses synthesized by copolymerization of hydroxy-ethylmethacrylate (HEMA) with ethylene glycol diamethacrylate (EGDM). Lenses constructed of such materials had hydrophilic properties with increased permeability to water, oxygen and low molecular weight constituents of tears, thereby providing metabolic advantages. Most recently, new lens materials have been introduced which are highly gas-permeable, and without any appreciable water content, such that extended wearing times can be achieved along with other various advantages.
In the use of contact lenses as an aid to a patient's vision, eye health has been and remains of major concern. Particularly, there is a need to supply oxygen to the corneal epithelium. This has been problematic with some of the materials utilized for fabricating corrective contact lenses. The corneal epithelium requires about eight percent (8%) oxygen for a proper aerobic glucose metabolism. The oxygen is supplied by the precorneal tear film naturally occurring in the eye. When wearing a corrective contact lens, the lens must either allow transmission of oxygen through the lens or must fit such that tear film exchange occurs beneath the lens. At the time of the blinking movement of the eye, tear exchange occurs by a pumping of tears from the tear reservoir. The corrective contact lens may facilitate this pumping action by means of lens movement during blinking. For proper eye health, the lid pumping action associated with corrective contact lenses may be necessary to prevent corneal anoxia.
With prescription contact lenses adapted to correct refractive error of an eye, various developments have been implemented to facilitate tear exchange or proper oxygen transmission to the cornea so as to maintain corneal health. Such designs include the rigid gas permeable contact lenses which allow transmission of gases through the lens to facilitate exchange of oxygen and carbon dioxide. One prescription contact lens design included a spiral vent lens having a design which theoretically provided a "jet propulsion" type of effect, wherein depressions in the concave surface of the lens were provided to produce rotation of the lens on the eye cornea so as to prevent tear fluid stagnation under the lens. Other corrective contact lens designs also provided means to promote tear exchange beneath the lens, which include the use of recesses, fenestrations or other various mechanical features to allow transmission of tear fluid into and out of the region beneath the contact lens. In each of these designs, tear exchange beneath the lens was of prime consideration so as to maintain eye corneal health while also allowing a more comfortable fit to facilitate the wearing of such lenses for longer periods of time. Many of these contact lens designs also relied upon the lid pumping action to accomplish the desired tear exchange.
Each of the above types of prescription contact lenses was conventionally designed to have a minimum thickness to also aid in comfortable wearing of the lenses. Such lenses, as well as many prescription contact lenses manufactured today, are typically between 0.10-0.30 mm, and allow the lid of the eye to close thereover. The minimum thickness of these lenses facilitates the desired pumping action and tear exchange beneath the lens.
As a completely distinct application from corrective lenses, contact lenses have also been used as an aid in diagnostic and surgical or laser treatment applications. A number of special contact lenses have thus been developed to assist eye care professionals in diagnosing and/or treating eye disease. Such diagnostic and therapeutic contact lenses may be used for corneal observation and for diagnosis of corneal abnormalities. Other diagnostic or therapeutic contact lenses include gonioscopy lenses which are designed for observation of the angle of the anterior chamber of the eye. Certain gonioscopy contact lenses are adapted to partially or completely neutralize the power of the cornea so as to enable observation of the anterior chamber angle directly or by means of mirrors. Gonioscopy lenses are generally utilized in conjunction with a slit lamp biomicroscope or other microscope, wherein light from a slit lamp is reflected into the anterior chamber angle, and returns along the same path to be viewed through the microscope.
Alternatively, diagnostic or therapeutic contact lenses may be used in observation of the ocular fundus when employed with a slit lamp biomicroscope or other microscope. Special contact lens have been developed for use in a technique known as direct ophthalmoscopy, wherein an erect virtual image of the retina is produced. Another diagnostic procedure, indirect ophthalmoscopy, may also utilize a contact lens system to form a real, inverted image of the fundus, which may then be viewed with a slit lamp biomicroscope or other microscope.
Diagnostic or therapeutic contact lenses have also been utilized in laser surgery, such as photocoagulation treatment, and particularly in iridectomy, trabeculotomy, capsulotomy, vitrectomy, and other treatment procedures. With the use of lasers in eye treatment, attention has been given to avoid the risk of damage by the laser beam to areas of the eye which are not intended to be treated. A contact lens may be utilized to minimize the amount of energy to those portions of the eye which are not to be treated. Anti-reflection coatings may be used on these optical lenses, which facilitate transmission of laser energy to the proper areas of the eye. Diagnostic or therapeutic lenses have been utilized to image the eye structure which is to be treated, so as to enable accurate location of the laser beam focus. Contact lenses may also be utilized to increase the cone angle of the laser beam so as to dissipate the energy of the laser beam both in front and beyond its focus so as to avoid damage to eye tissue adjacent the areas to be treated. These and other special contact lenses may therefore be used both to facilitate surgical techniques as well as to protect those portions of the eye from energy introduced by the laser beam.
In the use of such diagnostic or therapeutic contact lenses, an ophthalmic solution is conventionally utilized to fill any precorneal space between the diagnostic or therapeutic contact lens and the cornea of the eye being examined. The use of an artificial fluid may additionally aid in the prevention of oedema, which can interfere with observation and diagnosis. The ophthalmic solution may further facilitate translational movement of the diagnostic or therapeutic contact lens on the cornea for observation of different areas of the eye being examined. The ophthalmic solution also acts in conjunction with the diagnostic or therapeutic contact lens to essentially neutralize any corneal irregularities thus facilitating ophthalmoscopic or slit lamp examination of the eye. The diagnostic or therapeutic contact lens, in association with the ophthalmic solution, will essentially eliminate the refractive power of the cornea from the optical system.
Unfortunately, the use of ophthalmic solution in association with a diagnostic or therapeutic lens has been found to have many disadvantages. These disadvantages make use of diagnostic or therapeutic contact lenses by a practitioner difficult, or make the diagnostic or treatment procedures objectionable to a patient. The use of an ophthalmic solution in association with a diagnostic or therapeutic contact lens firstly creates the additional step of solution application which the practitioner must perform prior to diagnosis or treatment utilizing the lens instrument. The use of an ophthalmic solution adds another step in the diagnostic or therapeutic procedure and creates an additional expense to the practitioner. Additionally, residual ophthalmic solution from the diagnostic or therapeutic procedure may also remain and dry on the diagnostic or therapeutic contact lens, as well as the eyelids of the patient. This will again add to the steps which must be performed in the diagnostic procedure, in the removal of residual fluid after examination. Similarly, the patient's vision may be blurred after examination or treatment, as the ophthalmic solution remains on the eye and may require flushing or other cleaning procedures to clear and restore the patient's vision or to allow subsequent ocular photography.
Other problems associated with the use of an ophthalmic solution with a diagnostic or therapeutic contact lens include the possibility of producing corneal epithelial changes, which can result if the ophthalmic solution is not properly chemically balanced with respect to Ph and/or tonicity. These corneal epithelial changes may inhibit proper examination or observation of eye structures, and may further inhibit follow up diagnosis and/or treatment after initial examination. For example, fundus photography may not be possible as a result of epithelial changes caused by the use of the ophthalmic solution. Follow-up diagnosis or treatment procedures using contact or non-contact lens methods are many times desired to be performed by a practitioner subsequent to initial examination. With the use of an ophthalmic solution, follow up diagnosis or treatment may be more difficult, or may be impossible if using non-contact methods.
Another disadvantage of using an ophthalmic solution in association with a diagnostic or therapeutic contact lens is found in that air may be entrapped within the gel or solution in the precorneal space between the contact lens and the cornea of the eye being examined. These bubbles will inhibit proper examination or treatment using the contact lens. The formation of bubbles under the contact lens is a significant disadvantage of contact diagnostic and treatment procedures, and is created as a result of the use of an ophthalmic solution in the precorneal space between the contact lens and the cornea and/or the contact lens design. The formation of bubbles between the contact lens and the cornea will result in image distortion or blurring, as well as possible distortion of laser beam transmission through the lens.
Other problems associated with the use of an ophthalmic solution in association with a diagnostic or therapeutic contact lens are found in that the patient being examined must be positioned in an orientation such that the ophthalmic solution will remain in the precorneal space between the contact lens and cornea. Difficulty may be encountered if the patient's head is not in a vertical position, wherein upon the attempted application of the lens on the eye the ophthalmic solution may run out from the precorneal space and bubbles may form. Subsequent to diagnosis or treatment, the ophthalmic solution also is found to contribute to the suction of the lens on the cornea of the eye being examined, making the lens difficult to remove and causing discomfort to the patient.